Typically, phosphors are used in light-emitting devices such as display units such as vacuum fluorescent displays (VFD), field emission displays (FED), plasma display panels (PDP), cathode ray tubes (CRT), and light-emitting diodes (LED elements).
In each of these light-emitting devices, in order to cause the phosphor to emit light, it is necessary to supply some kind of energy to the phosphor in order to excite the phosphor. The phosphors are excited by a high-energy excitation source such as, for example, vacuum ultraviolet rays, ultraviolet rays, electron beams, blue light, and the like, and consequently emit visible light.
However, if conventional phosphors such as silicate phosphors, phosphate phosphors, aluminate phosphors, sulfide phosphors, and the like are used, then if these are exposed to the aforementioned types of excitation source, the problem arises that there is a reduction in the luminance of the phosphor.
Because of this, phosphors in which no reduction in luminance occurs even if they are exposed to these types of excitation source are being sought. Accordingly, oxynitride phosphors such as sialon phosphors have been proposed as phosphors in which there is little luminance reduction.
A sialon phosphor that contains Ca is disclosed in Patent document 1. Here, this sialon phosphor is manufactured via the manufacturing process described below.
Firstly, silicon nitride (Si3N4), aluminum nitride (AlN), calcium carbonate (CaCO3), and europium oxide (Eu2O3) are blended at a predetermined mol ratio. Next, the blended mixture is held for one hour at a temperature of 1700° C. in nitrogen at one atmosphere (i.e., 0.1 MPa). Firing is then performed thereon using a hot-press method, resulting in a sialon phosphor being manufactured.
The α-type sialon phosphor containing solid solution Eu ions which is obtained by this process is a phosphor that is excited by 450 to 500 nm blue light, and emits 550 to 600 nm yellow light. By combining this phosphor with blue LED elements, it is possible to manufacture white LED elements.
Patent document 2 concerns another sialon phosphor, and discloses a β-type sialon phosphor having a β-Si3N4 structure. Because this β-type sialon phosphor emits 500 to 600 nm green to orange light when it is excited by near-ultraviolet to blue light, it is favorably used as a phosphor for white LED elements.
Furthermore, an oxynitride phosphor formed by a JEM phase is disclosed in Patent document 3. This oxynitride phosphor is excited by near-ultraviolet to blue light, and emits light having an emission wavelength peak in a range of 460 to 510 nm. The excitation/emission wavelength range of this phosphor makes it favorable as a blue phosphor for a white LED which uses a near-ultraviolet LED as an excitation source.
In contrast, a white light-emitting diode obtained by combining a blue light-emitting diode element with a blue absorption/yellow emission phosphor is known as a conventional example of the light-emitting device technology used as an illumination device, and is put to use in various types of illumination.
For example, a white light-emitting diode obtained by combining a blue light-emitting diode element with a blue absorption/yellow emission phosphor is disclosed in Patent document 4. In addition, a light-emitting diode having the same type of structure is disclosed in Patent document 5. Furthermore, a light-emitting diode having the same type of structure is also disclosed in Patent document 6 as a light-emitting element which utilizes a wavelength conversion material.
Note that the phosphors which are used particularly often in these light-emitting diodes are represented by the general formula (Y, Gd)3(Al, Ga)5O12:Ce3+, and are yttrium-aluminum-garnet-based phosphors that are activated by cerium.
Moreover, a phosphor-equipped light-emitting diode which is provided with a semiconductor light-emitting element which emits either ultraviolet light or near-ultraviolet light and with a phosphor is disclosed in Patent document 7. This document discloses a structure in which, in this phosphor-equipped light-emitting diode, the semiconductor light-emitting element emits either ultraviolet light or near-ultraviolet light using pulse-shaped large current, and the phosphor which is formed as a film on the surface of the element is excited by the light emission of this semiconductor light-emitting element. In this structure, the emission color of this phosphor-equipped light-emitting diode can be switched between blue, green, or red light in accordance with the type of phosphor that is formed as a film on the surface of the element.
Moreover, a dot matrix type of display unit which is provided with a light-emitting layer which is formed by a III-group nitride semiconductor, and three types of phosphor layers that receive ultraviolet light having a peak wavelength of 380 nm for the wavelength of the light emitted from this light-emitting layer and then respectively emit light in the three primary colors of red, green and blue is disclosed in Patent document 8.
Furthermore, a semiconductor light-emitting element that emits white light using a semiconductor light-emitting element that emits light having a wavelength of 390 through 420 nm, and a phosphor that is excited by the light emitted from the semiconductor light-emitting element is disclosed in Patent document 9. Here, because the semiconductor light-emitting element emits light which has limited visibility to humans, the sensation is created that even if the intensity and wavelength of the light emitted by the semiconductor light-emitting element are varied there is substantially no change in the color tone. Moreover, light which has a wavelength of between 390 and 420 nm tends not to damage the device component elements such as the resin in which the phosphor is dispersed. In addition, generally, ultraviolet light has various harmful effects on the human body, however, because light having a wavelength of 390 nm or more is used, there are no harmful effects from leakage excitation light. In this case, phosphors of various oxides and sulfides are used for the phosphor that emits light upon being excited by light having a wavelength of between 390 and 420 nm.
Illumination devices such as these can be manufactured using a known method such as those described, for example, in Patent document 10 and Patent document 11.